Steroid, thyroid and retinoid hormones produce a diverse array of physiologic effects through the regulation of gene expression. Upon entering the cell, these hormones bind to a unique group of intracellular nuclear receptors which have been characterized as ligand-dependent transcription factors. This complex then moves into the nucleus where the receptor and its cognate ligand interact with the transcription preinitiation complex affecting its stability and ultimately the rate of transcription of the target genes.
The Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear hormone receptor subfamily of transcription factors. PPARs form heterodimers with other members of the nuclear hormone receptor superfamily and these heterodimers regulate the transcription of various genes. There are 3 known subtypes of PPARs, PPAR-alpha, PPAR-delta, and two isoforms of PPAR-gamma.
Peroxisome proliferator-activated receptor gamma, expressed primarily on the surface of adipocytes, is a multifunctional transcription factor which plays a central role in the control of insulin sensitivity via the regulation of adipocyte gene expression and differentiation in response to prostanoid and thiazolidinedione (TZDs) ligands (Brun et al., Curr. Opin. Lipidol., 1997, 8, 212-218; Shao and Lazar, J. Biol. Chem., 1997, 272, 21473-21478; Tontonoz et al., Curr. Opin. Genet. Dev., 1995, 5, 571-576). It has also been identified as a key player in the modulation of cellular transdifferentiation (Hu et al., Proc. Natl. Acad. Sci. U.S.A., 1995, 92, 9856-9860), terminal differentiation of cancer cells (Mueller et al., Mol. Cell, 1998, 1, 465-470; Tontonoz et al., Proc. Natl. Acad. Sci. U.S.A., 1997, 94, 237-241) and inflammatory processes (Jiang et al., Nature, 1998, 391, 82-86; Ricote et al., Nature, 1998, 391, 79-82; Su et al., J. Clin. Invest., 1999, 104, 383-389). The protein is also expressed in other tissues such as colon and breast epithelial cells, bone marrow, leukocytic cell lines and T-cells (Greene et al., Gene Expr., 1995, 4, 281-299), and, in macrophages, has been linked to the anti-inflammatory action of TZDs and their influence on the progression of atherosclerosis (Jiang et al., Nature, 1998, 391, 82-86; Ricote et al., Proc. Natl. Acad. Sci. U.S.A., 1998, 95, 7614-7619; Ricote et al., Nature, 1998, 391, 79-82).
The two isoforms of Peroxisome proliferator-activated receptor gamma, PPAR-gammal (PPARG1) and PPAR-gamma2 (PPARG2), result from alternate promoter usage and mRNA splicing (Greene et al., Adv. Exp. Med. Biol., 1997, 253-260; Greene et al., Gene Expr., 1995, 4, 281-299) and while PPARG1 is expressed in a range of tissues, PPARG2 is expressed exclusively in adipose tissue (Tontonoz et al., Cell, 1994, 79, 1147-1156). Disclosed in U.S. Pat. No. 5,686,596 are the DNA and polypeptide sequences of Peroxisome proliferator-activated receptor gamma (Mukherjee, 1997) while the sequences encoding the promoter regions are disclosed in the PCT publication WO 99/05161 (Briggs et al., 1999).
Elevated expression of Peroxisome proliferator-activated receptor gamma has been demonstrated in human primary and metastatic breast adenocarcinomas (Mueller et al., Mol. Cell, 1998, 1, 465-470) and in Alzheimer's disease brains (Kitamura et al., Biochem. Biophys. Res. Commun., 1999, 254, 582-586) while allelic variants have been reported in sporadic colon cancers (Sarraf et al., Mod. Cell., 1999, 3, 799-804). The pharmacological modulation of Peroxisome proliferator-activated receptor gamma expression and/or function may therefore be an appropriate point of therapeutic intervention in pathological conditions.
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of Peroxisome proliferator-activated receptor gamma. To date, investigative strategies aimed at modulating Peroxisome proliferator-activated receptor gamma function have involved the use of antibodies and the administration of synthetic and naturally occurring ligands that act as agonists.
Peroxisome proliferator-activated receptor gamma is activated by a range of synthetic and naturally occuring substances including thiazolidinediones (TZDs) (Kubota et al., Cancer Res., 1998, 58, 3344-3352; Lehmann et al., J. Biol. Chem., 1995, 270, 12953-12956; Mizukami and Taniguchi, Biochem. Biophys. Res. Commun., 1997, 240, 61-64; Murakami et al., Diabetes, 1998, 47, 1841-1847; Reginato et al., J. Biol. Chem., 1998, 273, 32679-32684; Spiegelman, Diabetes, 1998, 47, 507-514), phenylacetic acid derivatives (Berger et al., J. Biol. Chem., 1999, 274, 6718-6725; Elbrecht et al., J. Biol. Chem., 1999, 274, 7913-7922), fatty acids (Palmer and Wolf, FEBS Lett., 1998, 431, 476-480), prostaglandins (Forman et al., Cell, 1995, 83, 803-812; Kliewer et al., Cell, 1995, 83, 813-819) and components of oxidized low-density lipoproteins (Huang et al., Nature, 1999, 400, 378-382).
TZDs, agonists of Peroxisome proliferator-activated receptor gamma, are currently being developed as insulin sensitizers for the treatment of non-insulin dependent diabetes mellitus (NIDDM) as well as for the treatment of cardiovascular disorders, gastrointestinal disease and climacteric symptoms. Modulators of this type are disclosed in U.S. Pat. Nos. 5,902,726 and 5,814,647 as well as in the PCT publication WO 98/43081 (Kliewer et al., 1999; Lefebvre et al., 1998; Urban and Green, 1998). There remains, however, much controversy surrounding the mechanism of action and the safety of TZD-like compounds. In studies of colon cancer, conflicting results have been reported regarding the efficacy of TZD-like drugs (Lefebvre et al., Nat. Med., 1998, 4, 1053-1057; Saez et al., Nat. Med., 1998, 4, 1058-1061; Sarraf et al., Nat. Med., 1998, 4, 1046-1052).
Consequently, there remains a long felt need for additional agents capable of effectively inhibiting Peroxisome proliferator-activated receptor gamma function.
Antisense technology is emerging as an effective means for reducing the expression of specific gene products and may therefore prove to be uniquely useful in a number of therapeutic, diagnostic, and research applications for the modulation of Peroxisome proliferator-activated receptor gamma expression.
The present invention provides compositions and methods for modulating the expression of one or both splice variants of Peroxisome proliferator-activated receptor gamma.